In the testing of lung capacity and the ability of a person to inhale it is known to use an inhalation valve to produce a change or differential in air pressure which is pneumatically connected to a transducer to produce an electric voltage which is a function of the change or differential in air pressure. The change or differential in air pressure produced is not very great, and in the past this has required very sensitive transducers that have been quite expensive. One typical such transducer costs on the order of about $300.